Does ch. 4, pp. 36 ff., of the manual cover what you need? That's on balancing a mixed gas system. My intuition would be that total resistance and total pressure would have to be in balance, just like a straight CO2 system, regardless of the proportional contributions to pressure of each gas.* But I don't have expertise. (Unfortunately my only practical experience with nitro was changing kegs and pouring Guinness long ago, never had to design a system.)
* If it's a simple as that, balancing a direct draw system is earlier in the manual.